Conventionally, a photovoltaic module for collecting sunlight and converting it into electric power has been developed. For example, the following art is disclosed in Patent Document 1 (WO 2013/150031). That is, a concentrator photovoltaic device described in Patent Document 1 includes a lens and a power generation element in its case, wherein a distance between the lens and the power generation element is adjusted by introducing gas into the case.
Moreover, for example, the following art is disclosed in Patent Document 2 (U.S. Pat. No. 8,592,738).
That is, a device for checking the optical axis of incoming light is attached to a concentrator photovoltaic device described in Patent Document 2.
Next, for example, the following art is disclosed in Patent Document 3 (Japanese Patent Laying-Open No. 2008-84955). That is, a concentrator photovoltaic unit described in Patent Document 3 includes: a light-transmitting protection plate for protecting the top surface of the concentrator photovoltaic unit, a condensing lens for collecting sunlight being joined to the light-transmitting protection plate; an elongated frame serving as a base structure for the concentrator photovoltaic unit; and a solar cell mounted plate on which a plurality of solar cells are mounted. Moreover, the elongated frame is provided with an air hole at its end portion in the longitudinal direction to cause flow of air in the elongated frame.
Moreover, for example, the following art is disclosed in Patent Document 4 (Japanese Patent Laying-Open No. 2008-4661). That is, a concentrator photovoltaic device described in Patent Document 4 includes a case that is surrounded by a bottom member, a circumferential member, and an upper member to have a space therein and that is used such that the upper member is inclined to face the sun. The upper member of this case is provided with a plurality of Fresnel lenses for collecting sunlight. A plurality of photovoltaic cells are included in the case in order to receive the light collected by the Fresnel lenses to generate electric power. Moreover, the circumferential member of the case has opposing surfaces each provided with at least two openings. The two openings in each of the surfaces are disposed at the upper side and at the lower side. The upper side is closer to the Fresnel lenses, and the lower side is closer to the photovoltaic cells.